Polyalkyleneether-thioether glycols, having the structure EQU H--OC.sub.2 H.sub.4 SC.sub.2 H.sub.4 ].sub.x [OC.sub.4 H.sub.8 --.sub.y OH
wherein the mole ratio x:y ranges from about 45:55 to 60:40, respectively, are disclosed by Schwarz et al., U.S. P at. No. 2,844,566. Example 1 therein describes the preparation of a copolymer of thiodiethanol and 1,4-butanediol (1/1) having a molecular weight of about 930 (by hydroxyl number determination). Such copolymers, wherein the mole percentage of thiodiethanol represents 50% or less, are extremely difficult to prepare by conventional acid catalyzed condensation procedures; that is, the composition of the resulting polymer does not conform to the mole ratio of the monomers charged. The reason for this is that since the hydroxyl groups of thiodiethanol are activated by the central sulfur atom, there is a pronounced tendency for thiodiethanol to homopolymerize rather than copolymerize. Therefore, under normal conditions, the composition of Schwarz et al is mostly polythiodiethanol. This is true whether the alkanediol comonomer is 1,4-butanediol or any other alkanediol.
The product described by Schwarz et al not only contains large amounts of homopolythiodiethanol, thereby being quite different in composition from the macroglycols of the present invention, but also results from a process lacking in the critical extraction procedure of the present invention described below. Therefore, the macroglycol of Schwarz et al. does not yield polyurethane elastomers which exhibit the outstanding dynamic mechanical properties of those of the present invention.